Convection enhanced delivery (“CED”) of a bioactive agent involves introducing a fluid containing the bioactive agent into a patient's tissue under pressure so that the fluid moves through the tissue via bulk flow. Implementing CED generally involves inserting multiple catheters into the tissue to be treated, such as cerebral tissue. To reduce the risk of hemorrhage and/or trauma to the tissue and to reduce the risk of backflow (i.e., non-delivery into tissue parenchyma), it is desirable for the catheters to be microcatheters with small outside diameters.